A mechanical linear drive system having these characteristics is known from U.S. Pat. No. 4,512,208 (=German Patent No. 32 05 143). In this linear system, the threaded spindle is rotatably supported in the bearing means of the profiled tubular structure and can be coupled to an electric motor mounted externally on one of the bearing means. This linear system is distinguished by the fact that, among other advantages, the force transfer element can be positioned exactly, and large drive forces can be transferred. Since the linear movement of the force transfer element is automatically generated by the drive threaded spindle, however, it is fundamentally impossible to move a plurality of force transfer elements on one axis independently of one another. Furthermore, a variation in the speed of the linear movement of a force transfer element can be done only by varying the rotational speed of the threaded spindle accordingly.
However, there are applications in which it would be desirable to have a greater range of freedom in terms of the possible drive options for linear movements to be generated.
This is also applicable to a positioning drive means disclosed in German Utility Model DE-GM No. 81 32 113, which has a positioning spindle provided with an external thread and secured against rotation; this spindle is screwed into a nut element coupled to a motor via a slip coupling and a gear. The nut element is supported in a gear box such that it is axially immovable; by its rotation it axially displaces the positioning spindle. A further factor in this positioning drive means is that the axial adjustment of the positioning spindle precludes its accommodation in a profiled tube that would surround it over its entire length and thereby protect it from external influences. It is in no manner possible to derive the adjusting movement from more than a single drive means.